1. Field of the Invention
The present invention relates to the design and manufacture of novel microstructural shaped articles, including micro instruments such as micro-knives, tweezers, saws, pins, clamps, and hooks from very hard and chemically inert materials at low cost suitable for microsurgery.
2. Description of the Related Art
In microsurgery such as ophthamological surgery, small, precision, mechanical structures with sharp cutting edges are needed. In addition, many shapes and cutting edge variations such as serrated knives and interocular saws are needed for specialized surgery in the region of the eye. Further, it is important that these instruments be made of a mechanically stable material that is both hard and durable.
Conventionally, these "edged" medical tools are either mass produced from metals such as tungsten or stainless steel, or hand ground from harder materials such as diamond, silicon and sapphire. The disposable metal knives are relatively blunt and wear quickly over time. The non-disposable diamond or sapphire knives, on the other hand, are expensive and brittle. Further, current techniques of fabricating these harder knives are unable to produce certain cutting edge variations such as serrations that are needed in this type of surgery.
In particular, the current manufacturing technology for hand-made instruments of the above-described type is not only expensive, but also is limited in its ability to produce important second order structures such as serrations and inside angles.
U.S. patent application Ser. No. 08/822,021 filed 16 January 1992 in the names of Gary W. Jones, et al., the disclosure of which is hereby incorporated herein, describes a lithographic pattern and etched structural method of making such types of microinstruments. This technique, while an advance in the art, nonetheless suffers from a number of associated deficiencies, as discussed below.
Sapphire, ruby and silicon carbide are very difficult and expensive to etch because of the etch chemistry required. Inert metal masks such as platinum or iridium are necessary. These masks must be sufficiently thick to withstand highly reactive etches with reagents such as molten potassium hydroxide. Further, such method requires very expensive etch vessels constructed of materials such as platinum that are slowly consumed during the process. Alternative reactive ion etch (RIE) processes are very slow and expensive with the inert materials of choice.
In addition to the foregoing, angles of edges of the shaped product article are controlled by the crystal orientation of the above etchants which means some edges and serrations will be non-optimal. Further, 90 degree angles are usually desired at the base of these devices to provide a solid, non-cutting support. The aforementioned etching technique produces razor edges on at least some of those bases making stable mounting of such shaped articles more difficult.
Japanese Patent Kokai No. 63-92345 discloses an edged medical tool wherein the surface of the edge tool is provided with a carbonaceous coating layer of a diamond-like crystalline structure having a thickness of 1 to 20 nm. The diamond-like crystalline structure is deposited by the plasma-induced vapor-phase deposition in an atmosphere of a gaseous mixture of hydrogen and a hydrogen-containing compound such as methane.
U.S. Pat. No. 4,980,021 to Kitamura et al. describes etching of the diamond-like coating layer formed in a process such as that of Japanese Patent Kokai No. 63-92345, with a plasma of hydrogen gas to sufficient extent so that the surface of the edged tool has a roughness of 0.5 to 5 nm. Although this improves the incisiveness of the edged tool, the process starts with an existing shaped base body and therefore does not enable the fabrication of knives with serrations and other cutting variations that are needed in opthalmological surgery.
Microelectronic fabrication techniques have been developed in the field of semiconductors. U.S. Pat. No. 4,916,002 to Carver discloses a microminiature tip assembly which is fabricated using photolithography and anisotropic etching. The crystalline form of silicon is used to advantage by etching along the grain boundaries to form a pit in a silicon substrate. Tungsten is then deposited into the pit to form a sharp tip for use in a scanning tunneling microscope assembly.
Another microfabrication technique is disclosed in U.S. Pat. No. 4,740,410 to Muller, comprising a method of producing a micromechanical structure with two or more members measuring less than 1000 micrometers in any linear dimension. The disclosed technique provides sacrificial layers of material that are later etched away so that the mechanical members become movable relative to each other.
U.S. Pat. No 4,551,192 to DiMillia et al. discloses the use of a silicon carbide body in a pinchuck formed with microcircuit lithography. U.S. Pat. No. 4,911,782 to Brown discloses a miniature biological chamber made with photolithography.
U.S. Pat. No. 5,082,254 to Hunnell, et al. discloses a microtome object holder assembly useful for histology applications, which comprises a clamping member including a V-shaped channel which is formed by electrical discharge machining. Such machining utilizes a reverse image electrode formed of a suitable material such as copper, graphite, copper-tungsten, or the like. The electrical discharge electrode is placed in contact with a metal block to be machined to form a first clamping member. The requisite voltage is applied to produce electrical discharge arcing and erosion of the metal, to form the reverse image of the electrode profile in the resultingly machined metal block. In such manner, discharge electrodes are suitably formed with a reverse image of the desired profile contour, with the electrode being employed to "burn in" the desired contour profile.
Accordingly, it would be a significant advance in the art, and is an object of the present invention, to provide a shaped article and forming technique therefor which overcomes the above-discussed deficiencies, and is broadly applicable to a wide variety of materials of construction.
Another object of the present invention is to provide microsurgical knives in a variety of new and unique shapes, such as serrated knives and concavely shaped knives, and other compound contour shapes.